This invention relates to a pressure relief valve for regulating the oil pressure in a lubrication system of an internal-combustion engine. The valve has a basic cylindrical shape and is arranged in a bore of a housing. The valve includes an axially movable sealing part or valve body, with a sealing area or surface which is biased by a spring against a valve seat in the housing.
A known pressure lubrication system for an internal-combustion engine is shown in German Unexamined Patent Application No. E-OS 24 56 524 and includes a relief valve which is guided on a tube-type shaft and which has a conical sealing surface which is clamped against a corresponding valve seat by a spring.
This construction has the disadvantage that the usual process tolerances, especially between the valve stem guide and the valve seat, impair the function of the relief valve, in which case the elimination of such problems requires relatively large expenditures.
It is therefore an object of this invention to provide a pressure relief valve for the oil pressure of an internal-combustion engine lubrication system in such a way that tolerance variations which occur within the framework of conventional manufacturing processes do not detrimentally influence its proper functioning.
These and other objects are attained in a pressure relief valve according to the present invention which includes a housing, a valve body disposed within a bore in the housing, and a guide member which is non-fixedly arranged within the bore for guiding the movement of the valve body. The bore within the housing, the valve body, and the guide member are preferably cylindrical in shape. The valve body is axially movable within the bore and is provided with a sealing area or surface on one end thereof. A compression spring is provided for biasing the sealing surface of the valve body against a valve seat formed in the housing. In an especially preferred embodiment, the sealing surface of the valve body is spherically shaped, while the valve seat of the housing is conically shaped. This structure, in combination with the "floating" nature of the guide member, assures proper alignment and leak proof operation of the valve.
In the preferred embodiment shown in the drawings, the guide member is a cylindrical sleeve which is provided with a plurality of openings or passages in the vicinity of an outlet duct formed in the housing. The openings are preferably evenly distributed around the circumference of the guide sleeve. The outside diameter of the cylindrical sleeve is preferably reduced in the vicinity of the outlet duct.
In the preferred embodiment, a compression spring is provided for biasing the sealing surface of the valve body against the valve seat in the housing. The spring is positioned within a recess or bore in the valve body, and a corresponding recess in a threaded plug which secures the guide sleeve in the housing. The valve body and the guide member are preferably formed of materials which have similar coefficients of thermal expansion. A vent passage is provided in the cylindrically shaped guide sleeve to connect the spaces on either side of the sleeve wall with one another to equalized operational pressures within the bore.
The advantages that are mainly achieved by means of the invention are that, in the case of considerable but still permissible tolerances between the bore and the valve seat, the sealing part of the pressure relief valve still interacts with the valve seat in a leakproof manner due to the floating guide sleeve. In other words, the sealing part, via the sealing area and the valve seat, is aligned within the framework of the axial and radial play of the guide sleeve. This is effectively enhanced by the fact that the sealing area of the sealing part is spherically shaped, while the valve seat of the housing is conically shaped.
By means of the guide sleeve, it is also achieved that the sealing part is protected from manufacturing imperfections (e.g., burrs) at edges, such as those of the oil outlet duct, which are hard to remove and, in the case of a direct contact with moving valve bodies, can result in a blocking of the latter.
The arrangement of passage openings in the guide sleeve ensures a controlled flow of the lubricant into the outlet duct. The localized taper or constriction of the outside diameter of the guide sleeve, in the vicinity of the outlet duct, also serves this purpose.
The recesses in the sealing part and the plug contribute to the proper functioning of the compression spring. When the guide sleeve and the sealing part are formed of materials which have similar or identical coefficients of thermal expansion, both parts will interact well with one another when affected by temperature. This valve arrangement is also suited for installation in a light-metal housing having a coefficient of thermal expansion which is clearly different from that of the valve arrangement. The resulting differences in thermal expansion have no influence on the mobility of the sealing part. Also, the sealing part, the guide sleeve, the compression spring and the closing plug are components that are easy to manufacture and simple to mount.
Finally, by means of a vent passage, it is achieved that during the operation of the sealing part the compressible medium within the guide sleeve can escape into the bore in the housing.
The invention is explained in the drawings by means of an example and will be described in detail in the following.